Part 3

Water vapor is part of the atmosphere. Some of it is always present in the air. The amount of vapor that the air can hold depends upon the temperature. When the temperature is warm, the air will hold more water. For instance, at 100° F. a cubic foot of air will hold 19.79 grains of vapor; at 80° F., 10.95 grains; at 50° F., 4.09 grains, and 32° F., 2.17 grains. At 32° F. is the freezing point on the Fahrenheit scale.

Air containing as much water vapor as it can hold is saturated. If the air is suddenly cooled down, that is, if the temperature falls when the air is saturated, air molecules are contracted, and it must give up the water, which produces rain. The ocean and the Great Lakes are the source from which the air gets its water. It rises into the air in the form of vapor, that is, vapor rising from the surface of the water, and the wind distributes it over the land. Condensation turns it into clouds, and when it is over-saturated, or rather, when the temperature drops and the air is unable to retain any more water, then it forms into drops of water and falls as rain. When the clouds get into the air, below the freezing point of the water, the drops of water are changed into ice crystals or snow flakes.

When the ice crystals are just at the point of melting into water, due to the rise in temperature, the snowflakes lose their form and the result is sleet.

HOW CAN WE USE THESE FACTS?

So far we have described, in a general way, certain facts about the elements of the air, such as temperature, pressure, humidity, precipitation, evaporation, clouds, winds, etc., and these facts of the elements enter into a very interesting phase of weather observation which we will designate as prophesying without instruments or forecasting by physical science. When we come to the more interesting and scientific part of weather observation, we will drop the word “prophecy,” because the instruments that are used to measure these elements are going to indicate certain things to us that will lead you to more definite conclusions. Hence, the following observations are what have given an opportunity to the weather prophet or to those people who have been credited with some mysterious power to prophesy what the weather is going to be. They are not definite or conclusive, and they cannot always be depended upon, but they certainly are significant and interesting, and a description of weather would not be complete without a list in chronological order of a series of phenomena or physical signs of this character that have lead certain men to gain quite a reputation for prophesying what the weather is going to be.

APPEARANCES

Various appearances that come in the sky.

For instance, a good example is in the case of the thunder storm, which can be determined at least a few hours in advance, by the movement of the clouds and the forms they take. In every locality there is a direction that clouds take that forecasts bad weather, and there is a direction that clouds take that forecasts fair weather.

When you see a halo about the top of a mountain, you know that bad weather is expected. The same is true when a halo appears about the moon. This indicates rain, or if the lower clouds break up and the upper clouds, or a second light covering of clouds, are seen above the lower ones, it speaks for continued bad weather. In some localities if rainy weather is continuing for some time, and a certain change in wind sets in, it will indicate that good weather is coming.

These observations will be readily understood as being adapted for certain localities and are not general. It is always necessary that the observer adapt himself to these localities and study them, so that he can make prophecies accordingly. It should be borne in mind that these prophecies are only possible from one day to another.

WHAT THE CLOUDS INDICATE

When high clouds are seen crossing the sun or the moon in a different direction from the lower clouds, this indicates change of wind toward the direction of the higher clouds. When you see hard-edged clouds, look for wind. When you see delicate soft clouds, look for fine weather and probably moderate breeze or high breeze. When you see gloomy dark clouds in a blue sky, look for slight winds. When you see a bright blue sky through fine clouds that are soft and delicate, this indicates fine weather. When you see soft-looking clouds, you can expect less wind, but probably rain. But when the clouds become hard and ragged, tufted and rolling in appearance, stronger winds are coming. When you see small clouds that are inky looking, look for rain. When you see light clouds traveling across heavy hard masses of clouds, this indicates both wind and rain, but if the light scud clouds are alone, you may expect wind only. Misty clouds forming or hanging over the peaks of hills indicate both wind and rain. If during a rainy spell they ascend or disperse the weather is pretty certain to clear up. If there has been fine weather and you begin to see light streaks in the sky which are distant clouds, and they continue to increase and grow into cloudiness, this indicates rain.

SUNSET AS AN INDICATION

When the sun is setting and the sky in the west presents a color of whitish yellow or radiates out at a great height, rain can be looked for during the next night or day. Gaudy colors where clouds are definitely outlined indicate probably wind and rain.

Before setting, if the sun looks diffused and the color is a brilliant white, this forecasts storms. When the sun sets in a slightly purple sky and the color at the zenith is a bright blue, this indicates fine weather. A red sunset generally indicates good weather, whereas a ruddy or misty sunset indicates bad weather.

WHAT THE SKY INDICATES

When you see a dark, dismal sky, look for rain. A sky with a greenish hue, described as a sickly-looking sky, is an indication of both rain and wind. A sailor’s sky, which is red in the morning, means either wind or rain, and it makes no difference if the sky is cloudy or clear, if at sunset it is rosy, it indicates fine weather. A gray sky in the morning indicates fine weather. When daylight is first seen above a bank of clouds, look for a good stiff wind. Wind is indicated if we have a bright yellow sky in the morning, and rain is indicated if the sky takes on a pale yellow hue. If the sky turns bright yellow late in the afternoon, it generally indicates that rain is near at hand. Unusual colorations, particularly of deep intense color, indicate wind or rain.

The following appearances indicate a change in the weather: When the atmosphere is clear and crystalline and the stars appear extremely bright; when the background of the horizon seems to be pinned up against the foreground; when the clouds form into delicate white film-like mist way up overhead. (Fig. 33.)

WHAT FOG AND DEW INDICATE

Locality has considerable to do with what the fog indicates. As a rule, where you have fog, there is not much wind, and as a result it does not indicate stormy weather, unless the fog becomes heavy with overhanging sky, then it is apt to turn into rain, but a heavy fog with a light sky indicates fine weather. A fog in the morning generally indicates a fair day. A rising fog is a good indication for fair weather.

Dew is a pretty good sign of fine weather. When you can see and hear with remarkable clearness, and everything is calm and still, it is a pretty infallible sign that cold weather is due.

Frost may be looked for on clear, calm, cloudless nights, when the ground is apt to be cooler than the air.

INDICATIONS FROM CIRRUS CLOUDS

When these clouds suddenly appear in the sky on a clear summer day, they indicate wet weather. Especially if the weather ends turn upward, which means that the clouds are coming down. When moisture in the form of little drops cling to vegetation, it is a pretty good indication that there is apt to be more rain.

When the sky assumes the appearance of a gray mass and the sun is observed shining through, it is a pretty good indication that it will rain before night.

When overhead clouds are thick and grayish and the lower surface of them is lumpy, this is an indication of rain.

Whirlwinds of dust are also indications of rain.

THE MOON

The rings that we see formed about the moon are caused by the delicate white clouds through which the moon is shining.

THE RAINBOW

The morning rainbow indicates that a shower is in the west, but if the rainbow is in the east it indicates that the shower has passed over.

BIRDS AND STORMS

There are certain actions of birds that indicate many things pertaining to the weather that are interesting. It is probable that their ability to fly into the air gives them a view of the horizon, that by instinct they have been able to determine the atmospheric changes. For instance, it is well known that if birds of long flight remain at their base, it generally foretells a storm. The sudden silence of birds has been referred to a great many times preceding a storm.

Barnyard fowls do many peculiar things that foretell certain weather conditions. The crow flies low and in great circles, cawing loudly, before approaching rain.

Sometimes the house fly is a pretty good barometer. Generally before a storm they seem to light on everything, particularly persons, and we call them “sticky.” Generally at these times they congregate in swarms. Most everyone is familiar with the gnat. They are one of the few insects that gives us indications and good signs, and when you see them forming in groups and moving along in front of you, you may expect fair weather.

There are many other interesting facts and fairy tales about indications by animals and insects, but there is nothing scientific about them. It has been demonstrated that there is nothing conclusive to be drawn from such signs, so we will not attempt to waste pages of this book reiterating these fables.

Certain actions of insects and animals give indications and enable the weather prophet to prophesy. The spider is a good example of an insect prophet, and if you will observe him carefully, you will find that when stormy weather is going to come on he shortens his webs, and if he anticipates a long, hard storm, he not only shortens the strings that hold up the web, but he strengthens them as well, and vice-versa, when he anticipates fine weather, he lengthens his strands of the web. When you see the spider cease his activities and he hangs pretty close to his home, which is the center of the web, you will know that rain is approaching. On the other hand, if he continues to spread about during a storm, you can be pretty certain that it is not going to be of very long duration.

The frog is a good example of an animal prophet. There is a green frog which has been studied in Germany, which will come out of the water when rainy weather or cold is approaching. Some observers have placed these frogs in a glass jar with a landing provided so that he can come out of the water when he wants to, and he is always observed high and dry above the water several hours in advance of a storm.

DEFINITE CONCLUSIONS Forecasting Weather by Means of Instruments

The first part of this book may not appeal to you, if you are of a scientific trend of mind, but it is quite essential that you possess a knowledge of the fundamentals treated in the earlier pages in order to thoroughly understand the weather instruments we will now describe. These instruments are the scientific means of forecasting what the weather is going to be. They definitely indicate certain things, and from these indications you are going to be able to draw conclusions and become a scientist or meteorologist. The success that you attain will depend upon the accuracy of the instruments and the care you use in reading them. You will be able to rig up a Weather Bureau of your own, and the use of these instruments will interest anyone in a study of the weather.

THE WEATHER VANE

To make a forecast, it is essential from what we have already written, to know the direction of the wind, and to determine the direction we must have a weather vane. It is real important that the vane should be sensitive to the slightest movement of the wind and give actual wind directions. At the same time it must possess the property of steadiness, so that when it is set up it will be rigid.

Fig. 34 shows the standard weather vane used at all United States Weather Bureau Stations and Fig. 35 shows the Gilbert Weather Vane.

Fig. 35. The Gilbert weather vane consists of a metal arrow pointer and a metal rod eight inches long and five thirty-seconds of an inch in diameter. The rod is fastened by means of a few staples to the side of a pole, or whatever is to be used as a support for the vane. About three inches from the top of the rod is a collar with set screw, which is tightened, and the vane itself is then placed on the rod, the rod passing through the small angles A and B, between the sides of the vane. It will be found that the vane will swing freely on this support, and by constructing two crosspieces with letters N, S, E, and W at each end of the pieces, of course having N pointing directly north, the vane will swing around and show the direction of the wind.

The standard United States Weather Bureau type hardly needs explanation, as the illustration clearly shows all parts. It is the old, reliable, standard iron, combined wind vane and anemometer support complete, twenty feet high; iron contact box near base, improved roller bearings for six-foot vane; latter, with electrical contacts shown enlarged at the right. The vane is fastened securely to the roof of the building and held in a perfectly vertical position.

THE ANEMOMETER. Fig. 36

It is essential to know the velocity of the wind. This is determined by means of an instrument called the anemometer.

Fig. 36. The Standard U. S. Weather Bureau Station Anemometer.

This is the well-known standard Robinson Anemometer, now in universal use throughout the world for the registration of wind velocity, but of the latest improved construction. It records electrically the miles or kilometers, etc., of wind movements on a register. The standard pattern as furnished to Weather Bureau stations is made of brass, highly polished and finished, aluminum (or copper reinforced) cups, steel spindle with hard steel bearings, a ten-mile or kilometer indicator, electrical contacts, etc.

The four hollow hemispherical cups are mounted upon cross-arms at right angles to each other, with the open sections vertical and facing the same way around the circumference. The cross-arms are on a vertical axis, which has at its lower end an endless screw. This axis is supported so as to turn with as little friction as possible. The endless screw is in gear with a wheel which moves two dials registering the number of revolutions of the cups. The mechanisms are mounted in a suitable metal case with glass front, as shown in the illustration, well protected from the weather, the whole being designed for outdoor use.

The center of the cups moves with a velocity about one-third that of the wind which puts them in motion. The cups are four inches in diameter. The distance from center of cup to center of rotation or axis is 6.72 inches. Assuming that the wind-travel is exactly three times that of the center of the cup, the dials are marked to register miles of wind travel, five hundred revolutions of the cups corresponding to a mile.

The ratio of wind-travel to travel of cup is in reality variable, depending on the velocity of the wind. It is less for high than low velocities. It varies also with the dimensions of the instrument, being different for every different length of arm and diameter of cup.

On account of the great interference offered by buildings and other obstructions to the free movement of the wind, its velocity is much less in the vicinity of these obstructions than beyond; therefore, in selecting the location for an anemometer, preference should be given to the more elevated points in the vicinity of the station, and some rigid support should be used to raise the instrument as far as practicable above the immediate influence of the office building itself. The support must be set up so that the anemometer on top or on the cross-arm is as nearly vertical as possible.

The illustration shows clearly the appearance of an approved Weather Bureau pattern combined support for wind instruments, similar to the one installed at our plant.

Fig. 37. The Gilbert Anemometer.

The Gilbert Anemometer consists of a case containing a spindle passing through a worm gear, which turns a toothed gear. This gear in its rotary motion makes a contact with a brass brush, which is connected electrically with a flashlight. The cross-arms, with cups attached, is placed on the spindle, and as the wind blows, it revolves the cups, causing the contact. The velocity of the wind is determined by counting the flashes for fifteen seconds, thus giving you the number of miles per hour. For instance, if light flashes eight times in fifteen seconds, this signifies that the wind is blowing eight miles an hour.

Fig. 38. How to Connect the Gilbert Anemometer.

By referring to the diagram, you will see that one wire which should be the annunciator wire, or even a small electric light wire, is connected from the wire at the anemometer case directly to one side of the lamp socket. Another piece of the same size wire connects the other side of the lamp socket to one terminal of your switch. The second terminal of the switch should be connected to an outer post of one dry battery. The inner post of this same dry battery should be connected to the outer post of the second dry battery. Complete the circuit by connecting the inner post of the second dry battery to any one of the screws at the bottom of the anemometer case. The lamp used should be a small flashlight battery lamp for use on two and a half to three volts. Be sure in making the connections that the ends of your wire are scraped free from insulation and dirt. This can be done by cutting off the insulation with a knife and then rubbing the copper wire bright by a piece of sandpaper or emery cloth, or even a file. The switch should be left open when you are not taking readings, in order to prolong the life of your batteries. By unloosening the little screw in the hub of the anemometer vanes, you can remove them and also take off the brass cap on the anemometer case. This should be taken apart once or twice a month, and some machine oil used around the bearings to keep them from wearing out too quickly.

THE STANDARD ELECTRICAL SUNSHINE RECORDER AND THE GILBERT SUNSHINE RECORDER

Fig. 39. The standard sunshine recorder is designed for recording the duration of sunshine electrically, continuously, and automatically, on a register. The instrument is essentially a differential air thermometer in the form of a straight glass tube with cylindrical bulbs at each end, enclosed in a protecting glass sheath, with suitable platinum wire electrodes fused in at the center, the whole mounted in a metal socket on an adjustable support.

The base is secured to the support on the roof so that the glass tube points north and south, with the blackened bulb toward the south and lowermost, then the tube is inclined at such an angle that the instrument will begin and cease to record sunshine with the proper degree of cloudiness. This inclination should be approximately 45° from the vertical. The machine should be adjusted at an hour when the sun is wholly obscured.

In temperate and cold climates, slightly different adjustments will be found necessary at different seasons of the year.

Fig. 40. The Gilbert Sunshine Recorder consists of a metal case, cylindrical in form, with a piece of metal turned up on the ends, dividing the cylinder in half. On each side of the case are small holes through which the sun casts its rays and records its movement and duration on a small piece of blue print paper inside the cylinder, one piece of paper being in each compartment. When the blue print paper is dipped in water, it becomes entirely bleached, with the exception of the path made by the sun, which shows up in a blue line.

The sunshine recorder should be set up so that the ends point directly north and south. The holes pierced in the sides of the case are nearer one end than the other. The end that the holes are nearest should be toward the south. It should be held firmly in place.

THE BAROMETER

The barometer is used for measuring the pressure of the atmosphere. The principle of this instrument was first discovered by Torricelli, a pupil of Galileo, the great Italian philosopher and scientist, in 1643. Many and various types of instruments have been made, but the two most generally used, especially where accurate indications are desired, are the mercurial and aneroid barometers. Either of these instruments are quite sensitive to changes in the weight or pressure of the earth’s atmosphere, and from their variations we are able to draw conclusions relative to changes in the weather. Figs. No. 41 and 42 illustrate the standard mercurial and aneroid barometers used most extensively today. A description of these barometers will serve to make the photographs clearer to the readers of this text.

THE MERCURIAL BAROMETER (Fig. 41)

The mercurial barometer in use today is practically the same as that invented by Torricelli. Of course, many changes have been made in the case containing the tube of mercury, adding to its attractiveness, but the principle remains the same.

The standard mercurial barometer consists of a straight glass tube about thirty-two or thirty-three inches in length, hermetically sealed at one end. The tube is of half-inch bore and is filled with chemically pure mercury, which has been boiled in the tube to insure the total exclusion of all air and moisture. After the tube has been filled, the open end is immersed in a cistern of mercury. Upon immersion the mercury drops in the tube to a height of 29.92 inches at sea level, or until counterbalanced by the weight of the surrounding atmosphere pressing upon the surface of the mercury in the cistern. The space in the top of the tube is a perfect vacuum and is called the Torricellian vacuum.